Preventing the marring of aluminum in vise jaws, parallels

chris.trotter

chris.trotter

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So I've run into a new issue - while I am flycutting/squaring up my aluminum stock, I'm marring the faces with the vise jaws and parallels. I had stoned the vise jaws previously. The parallels when I'm smacking it flat, the vise jaws are hit/miss as to whether or not they mar.

What's the correct way to deal with this?

apr19-surface_marring.png
 
Well....that is a curious question. You imply it's normal to have marred starting stock...? These are pieces i'm flycutting to square, to give me a clear starting point on my project.

I could re-face once done, but I'd have similar issues, no?
 
You missed the point::

Most of the time, square stock get machined to final shapes and sizes, and those mars will disappear when the metal is re-cut.
While this is happening, you are continuing to use parallels, and knock the stock onto the parallels. So whatever you are doing to cause those mars, will continue to be present all the way through the end of the machining. So mars will always be present.
 
I think we're saying the same thing. So how do you prevent marring in general is maybe the better question?
 
Chris, the issue you're having is probably due to tapping down to get the work solidly down on the parallels and the tops of the jaws are digging into the work. The work is not yet square so naturally the jaws dig in. This is a technique issue.

Try this.
  • Find a round rod, ideally aluminum, and put it between the work and the moving jaw of the vise. Try to place the flattest face of the work against the fixed jaw, insert the rod so it lies parallel with the bed of the vise and tighten the vise. The rod holds the flattest face against the fixed vise of the jaw but allows it to tilt a bit if that face is off square, which it is. Fly cut the top.
  • Turn the work so the flycut surface is against the fixed jaw and the bottom of the piece resting on the bottom of the vise or a single parallel sitting against the fixed jaw; this first flycut surface is now your reference surface. Re-insert the rod and lock it down, then flycut the second face; this second face is now 90 degrees to the reference surface.
  • Flip the piece 180 degrees with the reference face still against the fixed jaw; insert the round rod and lightly close the jaw, then tap the second face you cut into firm contact with the vise bed or single parallel and flycut the third face. Now you have three faces all 90 degrees to each other.
  • Remove the rod, put the reference face on the bottom of the vise or on two parallels if it is thin, then lock the piece in the vise. You now have three square sides and when you clamp down, nothing digs in. Flycut the top and you now have four square sides.
  • You can now either switch to an end mill and square the ends or stand the work vertically in the vise with the reference face against the fixed jaw; use a square to ensure the sides are vertical and fly cut the first end. Once that is square, flip it 180 degrees, put the fly cut end on the bottom of the vise and fly cut the last end.
You should now have a square work piece with no marring.

No mystery here. Just proper technique for squaring a rough work piece. Some of us use a ball bearing with a flat ground on one side that goes against the movable jaw instead of a rod; it works but the rod is easier to grab and use if the work piece is not too out of square. The ball works better for really rough stock where nothing is close to square. One more thing: after fly cutting each face, deburr the edges before re-clamping it in the vise.
 
Wire EDM, in this method of machining the tool never contacts the work so it requires little or no clamping force, this will solve your problems yet has drawbacks of its own as you might imagine.
 
@mikey that is exactly the process I was doing (although your explanation has been the clearest I've seen on this subject so far), the marring is happening when I'm hammering the piece into place on the vise. When I have two parallels under the reference surface, the front parallel is loose until I really mash on the workpiece with a deadblow hammer (made extra difficult because my mill is tiny). Further, when you say 'lightly tighten the vise and tap with hammer', this doesn't work. When I fully tighten the vise the front side lifts - my vise is really a glorified drill press unit. I suspect the only way to get past that is to get me a decent vise.

The card stock trick might help, though, given that I have to mash it - worth a shot.

Also lol at wire edm. When I was in college, we did a tour of a plant doing wire edm, super cool stuff. Massively outside the capabilities of my humble home shop, however. :D If there's gonna be another large machine, it'll be a surface grinder.
 
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